When installing a new car Battery or replacing an old one, it is important to connect the terminals correctly. 

However, many people are not sure which terminal to connect to first – positive or negative.

Car batteries are essential components of a vehicle's electrical system. 

They provide power to start the engine and supply electricity to other systems such as lights, radio, and air conditioning. 

However, when it comes to replacing or installing a new car battery, there is a common question that arises: 

Which terminal - positive or negative - should be connected first? In this article, we will discuss the answer to this question and the reasons behind it.

Which terminal Positive or Negative should be connected First When Installing a new Battery on the Car?

The Short Answer: Connect the Positive Terminal First

The general rule of thumb when installing a car battery is to connect the positive terminal first.

 The positive terminal is usually marked with a plus (+) sign and is typically larger than the Negative Terminal, which is marked with a minus (-) sign. 

By connecting the positive terminal first, you will ensure that there is no accidental contact with the negative terminal, which could cause a short circuit or even a spark that could ignite the battery gases.

Why Connect the Positive Terminal First?

There are several reasons why connecting the positive terminal first is recommended when installing a car battery. 

Here are some of them:

• Safety
• Easier to Access
• Prevents Damage to the Electrical System

Safety

As mentioned earlier, connecting the positive terminal first ensures that there is no accidental contact with the negative terminal.

Which could cause a short circuit or spark. This is because the negative terminal is connected to the car's chassis or ground.

This means that it is always live and could potentially cause a dangerous situation if not handled correctly.

Easier to Access 

The positive terminal is usually easier to access than the negative terminal, especially in newer cars where the battery is often located in a tight space. 

By connecting the positive terminal first, you can easily access the negative terminal without having to struggle with the positive cable in the way.

Prevents Damage to the Electrical System

By connecting the positive terminal first, you will also prevent any electrical damage to the car's electrical system. This is because some car systems, such as the airbag system, may be sensitive to voltage spikes that could occur if the negative terminal is connected first.

What About Disconnecting the Battery?

The same rule applies when disconnecting a car battery. 

You should always disconnect the negative terminal first, followed by the positive terminal. 

By disconnecting the negative terminal first, you will ensure that there is no electrical current flowing through the car's electrical system, which could potentially cause damage to sensitive components.

What happens if you connect the negative terminal first?

Connecting the negative terminal first when installing a battery or electrical component can sometimes be dangerous and result in a short circuit or electrical arc.

In most cases, it is recommended to connect the positive terminal first and then the negative terminal. 

This is because the negative terminal is often connected to the ground or the frame of the device, and if it is connected first, there is a risk of creating a circuit with the tool being used to connect it, which could cause a spark or short circuit. 

This can be particularly dangerous if the battery or electrical component being installed has a high voltage or amperage.

If the negative terminal is connected first, and then the positive terminal, the risk of a short circuit or spark is reduced, but it is still not recommended. 

It is always best to follow the manufacturer's instructions or the standard electrical safety practices to ensure the safe and proper installation of batteries and electrical components.

How do you properly install a car battery?

Installing a car battery requires some basic knowledge and safety precautions. 

Here are the steps to properly install a car battery:

• Gather the Tools and Equipment
• Open the Hood
• Locate the Battery
• Disconnect the Old Battery
• Clean the Battery Terminals
• Install the New Battery
• Check the Battery Installation
• Dispose of the Old Battery

Gather the Tools and Equipment

You will need a pair of gloves, safety goggles, a socket wrench, and a wire brush to clean the battery terminals.

Park the car in a safe and well-ventilated area: Turn off the engine and make sure all electrical components, including lights and radio, are turned off.

Open the Hood

Use the latch inside the car to open the hood.

Locate the Battery

The battery is usually located on one side of the engine bay and is a rectangular-shaped box with two terminals positive and negative sticking out of the top.

Connect the Positive Terminal First

The positive terminal on a car battery is usually marked with a “+” sign. Connect the positive terminal of the new battery to the positive cable of the car using a wrench or pliers.

Tighten the connection securely to ensure that it does not come loose.

Connect the Negative Terminal Second

The negative terminal on a car battery is usually marked with an “-” sign. 

Connect the negative terminal of the new battery to the negative cable of the car using a wrench or pliers. 

Tighten the connection securely to ensure that it does not come loose.

Disconnect the Old Battery

Use a socket wrench to loosen and remove the negative terminal (black) cable from the battery first, then the positive terminal (red) cable. 

Remove any brackets or clamps holding the battery in place and carefully lift the battery out of the engine bay.

Clean the Battery Terminals

Use a wire brush to clean the battery terminals and cable connectors. This will help ensure a good electrical connection.

Install the New Battery

Place the new battery in the same position as the old one, making sure it is securely held in place by any brackets or clamps. 

Connect the positive (red) cable to the positive terminal first, then the negative (black) cable to the negative terminal. 

Tighten the cable connectors with a socket wrench.

Check the Battery Installation

Make sure the battery is securely installed and the cable connections are tight. 

Start the engine and check that all electrical components are functioning properly.

Dispose of the Old Battery

Car batteries contain hazardous materials, so it is important to dispose of the old battery properly. Most auto parts stores or repair shops will recycle old batteries for you.

It is important to follow these steps carefully and take appropriate safety precautions when installing a car battery to prevent accidents and ensure proper installation.

What happens if you disconnect the battery while the car is running?

If you disconnect the battery while the car is running, it can cause several problems and potentially damage the electrical system of the vehicle.

Firstly, disconnecting the battery will cause the electrical system to lose its source of power, and the engine may stall immediately or shortly after. 

This is because the battery provides power to the engine's ignition system, and without it, the spark plugs will stop firing, causing the engine to shut off.

Secondly, disconnecting the battery while the engine is running can cause a voltage spike or surge in the electrical system, which can damage sensitive electronic components such as the alternator, voltage regulator, or the Engine Control Module (ECM). 

These components rely on a stable and consistent flow of electricity, and sudden changes in voltage can cause them to fail.

Lastly, modern cars are equipped with various safety features that rely on the battery to function correctly, such as airbags, anti-lock brakes, and stability control systems.

Disconnecting the battery while the car is running can cause these safety features to malfunction or not work at all, which can be dangerous and put the driver and passengers at risk.

Therefore, it is not recommended to disconnect the battery while the car is running. If you need to disconnect the battery for any reason, always turn off the engine first and take the necessary safety precautions to avoid any electrical shocks or sparks.

Final Thought

When installing a car battery, it is crucial to always connect the positive terminal first and then the negative terminal. 

This is because the positive terminal is typically connected to the vehicle's electrical system, which can cause a spark or electrical discharge when connected or disconnected.

 Connecting the negative terminal first can create a short circuit, potentially damaging the battery, and electrical system, or even causing injury. 

By connecting the positive terminal first and then the negative, you can minimize the risk of any accidents or damage, ensuring a safe and successful installation. 

Always remember to double-check the manufacturer's instructions and wear appropriate safety equipment when working with car batteries.

Thank You.